High speed bright nickel plating and electrolyte therefor

ABSTRACT

A METHOD OF HIGH SPEED ELECTROPLATING BRIGHT NICKEL DEPOSITS. THE BATH COMPRISES PHENYLPROPIOLAMIDE AS BRIGHTNER AND LEVELER AND MAY ADDITIONALLY CONTAIN SULFO-OXYGEN COMPOUNDS SUCH AS SACCHARIN. HIGH CURRENT DENSITIES AND HIGH ELECTROLYTE FLOW RATES ARE USED SIMULTANEOUSLY TO ACHIEVE A HIGH RATE OF NICKEL DEPOSITION.

United States Patent 3,576,725 HIGH SPEED BRIGHT NICKEL PLATING AND ELECTROLYTE THEREFOR Frank Passal, Detroit, Mich., assignor to M & T Chemicals Inc., New York, N.Y. No Drawing. Filed June 7, 1963, Ser. No. 286,170 Int. Cl. C23b 5/08, 5/46 US. Cl. 20449 4 Claims ABSTRACT OF THE DISCLOSURE A method of high speed electroplating bright nickel deposits. The bath comprises phenylpropiolamide as brightner and leveler and may additionally contain sulfo-oxygen compounds such as saccharin. High current densities and high electrolyte flow rates are used simultaneously to achieve a high rate of nickel deposition.

This invention relates to a novel process for electroplating. More specifically, it relates to high speed bright nickel plating.

As is well known to those skilled in the art, bright nickel plate may be obtained by plating from various types of baths, typically Watts-nickel baths, or modified Wattsnickel baths, or high-chloride nickel plating baths. Operation in these prior art baths typically may include plating from the nickel-containing solution at current densities which may be 1-10 amperes per square decimeter (hereinafter abbreviated as a.s.d.). Commonly these baths may contain a Wide variety of brightening additives-usually a combination of two or more additives which are necessary to obtain a bright, leveled deposit.

Under normal prior art nickel plating conditions, it may be possible toattain the desired plate having a thickness of 0.2-2 mils in a period of time which depends upon the current density and other conditions of operation. (One mil is 0.001 inch or 0.0254 mm.) Commonly production of a 1 mil plate requires for example at least minutes and possibly as long as one hour with the normally used current densities of 8 and 2 a.s.d., respectively. Normally nickel plating operations are conducted with little or moderate agitation i.e. low relative velocity between the bath and the cathode. Typically this may be effected by use of a slowly moving cathode bar, by air agitation, or combinations of both. Such agitation is normally sufficient to replenish the nickel ion content in the cathode film, at the current densities normally used.

Although it may be possible to obtain satisfactory bright nickel plate by use of such prior art systems, it has been found that production rates are undesirably low because of the time required, typically minutes to attain a one-mil plate. Furthermore, because of this slow rate of plate deposition, it is necessary to employ relatively large tanks which cover an inordinately large amount of expensive fioor space.

Typical prior art attempts which have been made to produce bright, leveled nickel deposits at high speed under varying conditions have included the use at high current densities of additive systems otherwise successful at ordinary plating speeds using low current densities. These have been unsuccessful because the prior art brightening systems did not permit attainment of highspeed, bright, and adequately leveled deposits over a wide current density range. These previous attempts to attain such deposits have involved the use of various cooperating additives including primary brighteners, secondary brighteners, or auxiliary brightening materials.

A secondary brightener may be a material which when added to a nickel plating bath in relatively high concentrations, typically l-30 g./l., produces a plate which is characterized by a refined grain structure and moderate luster, but which is not highly reflective. A primary brightener may be a material which, when present in amounts of the general order of magnitude of 5-200 mg./l. and used simultaneously with a secondary brightener will permit attainment of a highly reflective deposit over a wide and useful current density rangeln some systems, a third material, a secondary auxiliary brightener, usually in concentrations of 0.1-4 g./l. may be added to further enhance the luster and, particularly, leveling of the deposits.

Despite the numerous prior art attempts to develop a high speed bright nickel plating system which would have widely recognized advantages, there is today no commercially acceptable technique by which this can be accomplished. Although it may be possible by some processes to get an adequate degree of luster, it has not proven possible to concomitantly attain a high degree of leveling.

It is an object of this invention to provide a novel high speed technique for obtaining a bright nickel plate characterized by its high brilliance and extraordinary leveling. It is a further object of this invention to provide a high speed nickel plating system which may permit attainment of a ductile plate. Other objects will be apparent to those skilled in the art from inspection of the following description.

In accordance with certain of its aspects, the method of this invention for high speed electroplating a bright nickel deposit comprises electroplating said nickel deposit from a nickel bath containing a brightening and leveling amount of phenylpropiolamide, maintaining the cathode current density during said plating at a level of at least 10 a.s.d., and maintaining a high relative velocity between said nickel bath and said cathode thereby obtaining a highly lustrous, leveled nickel plate over a wide cathode current density range.

The nickel baths which may be employed in practice of this invention may include Watts-type baths, modified Watts-type baths, high-chloride baths, chloride-free baths, sulfamate-containing baths, etc. A typical Watts bath may have the following composition (here as elsewhere g./l. means grams per liter):

Amount, Preferred,

Component g./l

Nickel sulfate 250-500 300-407 Nlckel chloride 30-75 60-75 Boric acid 20-60 40-50 A typical modified Watts bath may have the following composition Amount, Preferred, g /l. g./l.

C omponent Nickel sulfate 250-500 300-400 Nickel chloride -150 -130 Boric acid 20-60 40-50 Amount, Preferred, Component g./ g./l.

Nickel Sulfate 250-500 300-400 Boric acid 20-60 40-50 In the above systems, soluble nickel anodes may be employed with the Watts or modified Watts baths. With the chloride-free systems, the anodes may be either soluble It is a particular feature of certain aspects of this inor insoluble. If nickel is used as the anode, it is preferably vention that it may be possible to attain a high-speed of electrolytic nickel containing a controlled amount of bright nickel deposit characterized by extraordinary desulfur, typically the SD type of nickel manufactured by gree of leveling, extremely high brilliance, and, particu- International Nickel Co. This type of anode permits operalarly, by unexpectedly high ductility (especially in chlotion with minimum amount of polarization and oxygen ride-free systems) by use of baths containing phenylproevolution in chloride-free baths. If insoluble anodes are piolamide together with a secondary brightener. In this desired, it may be preferred to use lead as the anode maembodiment, the brightening and leveling amount of terial; and this may usually require replenishment of phenylpropiolamide may be 0.2-0.6 g./l., and typically nickel content of the bath and reestablishment of proper 0.3 to 0.5 g./l. The preferred concentration of phenylbath pH by addition of a basic nickel compound e.g. propiolamide may be 0.4 g./l.

nickel carbonate, nickel hydroxide, etc. Among the types of secondary brighteners which may In p actice f th s invention it is preferred to add be employed may be aromatic sulfonates, sulfonamides, brightening and leveling quantities of phenylpropiolamide. lfi id or o bi atio thereof, Typical of th amyp y this Compound, when p y as the brightenmatic sulfonates may be benzene monosulfonate, naphing and leveling agent, y be P entin amounts Of at thalene 1,3,6-trisulfonate, and naphthalene 1,5-disulfonate. least It is preferred to maintaln t t compound Typical of the aromatic sulfonamides may be para-toluene Present in amount below its Solubility llmlt, Whleh, at sulfonamide and dibenzene sulfonamide. Typical of the yp Operating temperatures of w maybe aromatic sulfimides may be saccharin. When phenylproabout Thus commonly phenylproplolemlde piolamide is used in this embodiment together with a secy b p f in amount of about 1n the ondary brightener, the preferred secondary brighteners noted lllllstfatlve batbsmay include 1-4 g./l. of saccharin (Na salt) and 1-4 It is a feature of this invention that it may be possible f dibenzene 1f mide to attain high-speed nickel deposits characterized by Typically the secondary brighteners may be present in their extraordinary leveling characteristics together with concgntration of 1 f r bl 1 w eXtremelY high brilliance by use of baths Contammg the preferred secondary brightener, saccharin, is employed, phenylpropiolamide alone i.e. as the sole brightening and it may b6 present in amount f g 1 leveling additive. In this embodiment, the brightening and A typical bath which may be used in practice of this leveling amount of Phenylpropiolamide may be at least embodiment of the. invention may have the following comabout 0.8 g./l. up to saturation. Saturation typically may position: be 0.9-1.0 g./l. depending upon the temperature, which may be within the range 60 C.-80 C.

It is a further feature of this invention that the nickel Amount Preferred plating bath may be self-regulating as to maintenance of Component g-ll. g./l. the additive concentration level, i.e. the phenylproplol- Nickel 5111MB 250 500 375 amide, when present as the sole additive, may be present Nlckelelilorlden- 75-150 110 h th olid Borlc aold 20-60 45 in amount in excess of its solubility in w 1c case e s phenylpmpwlaml 0 0 4 phase may dissolve as the compound is consumed from saccharin (Na salt)- 1-4 3 solution as by cathode effects including reductive action.

Preferably the solid may not be maintained in the solution proper, but may be maintained in a cartridge or filter Another yp bath fvllleh may be used In pfaetleeot through which the plating solution may pass e.g. as it i this embodiment of the invention may have the following pumped to and from the plating bath. composition:

A typical bath or solution may have the following com osition:

p Amount, Preferred, Component g./l. g./l.

lgl'ickel sufate 25%?28 320 Amount, Preferred, one am 5 Phenylpropiolamlde 0. 2-0.6 0.4 Component g ,1 g ,1 saccharin (Na salt) 1-4 3 Nickel sulfate 250-500 375 Nick -150 Borle a 2 0-60 45 Phenylpmpmlamide Another typical bath which may be used in practice of 1 Saturation. this embodiment of the invention may have the following Another typical bath or solution may have the follow- 55 Composition: ing composition:

Amount, Preferred,

Amount, Preferred. Component ompnent 6O Iglickel sfifamate zlg gg 325 oric ac 45 g l lg 2 28 22 Nickel chloride (optional) 7. 5-15 15 or 0 r l 0 Phenylproplolamide 0. 2-0. 6 0. 4 Phenylpropwlanude. 0. 8 9 saccharin (Na Salt) 14 3 1 Saturation.

Another typical bath or solution may have the follow- 6 he typic l bath which may be used in practice of ing composition: this embodiment of the invention may have the following composition:

0 t Amount, Preferred, 7 O

omponen Amount, Preferred, giclizel s rameie alg lgg 32:; Component -l -l or 0 ac 5 Nickel chloride (optional). 7. 5-4 15 ggi gig figg Phenylpmpmlamlde Phen l rJi'lEriiiii'. 0 2-0.6 0 4 Saccharin Na salt 2-4 3 Saturation. 7

Another typical bath may have the following composition:

In practice of this invention, a metal cathode which has been precleaned and which may have been copper plated may be placed within a nickel plating bath together with either a soluble anode or an insoluble anode as hereinbefore described. Typical preferred temperature of the bath during plating may be 60 C.-80 C.

In the preferred practice of this invention, the baths are preferably maintained at a pH of 2-5, preferably 3.5-4.5, say 4. It is a concomitant advantage of the additive systems of this invention that the baths are operative over a very wide pH range in contrast to prior art brightener systems where much more limited pH ranges are necessary. This insensitivity to pH is of particular importance where insoluble anodes are used, necessitating pH adjustment with a basic nickel compound. Since these basic nickel compounds are most highly reactive below pH 3.5 it is highly advantageous to be able to operate substantially below pH 3.5. It is not necessary to use wetting or anti-pitting agents when plating according to this invention thereby minimizing problems which might arise therefrom because of e.g. foaming, decomposition products of wetting agents, etc.

During plating, the cathode current density will preferably be maintained at a level of at least about a.s.d. Preferably it will be found that the high-speed bright nickel plating process of this invention may be effected at a current density of 20-120, preferably 20-60 a.s.d. Plating carried out in accordance with this novel technique may permit deposition of predetermined thicknesses of bright, leveled nickel in a time which is as little as 10% or less of the time required when using standard processes presently available. Typically production of a bright nickel plate 1 mil thick by the process of this invention may require 3 minutes in contrast to 30 minutes for prior art plating processes. The rate of plating may typically be 1-3 minutes per mil of bright nickel plate.

The novel technique of this invention includes the step of maintaining a high relative velocity between the nickel bath and the cathode. It may be possible to maintain this high relative velocity which serves to replenish the cathode film with nickel ions as they are plated out therefrom, by use of a bath which contains agitation means sufiicient to maintain a substantially homogeneous catholyte. Typically this may be accomplished by use of high speed mixers in the solution.

It is preferred to maintain the high relative velocity between the nickel bath and the cathode at a level equivalent to about 60-320, say 150 cm./second. These velocities may be produced e.g. by varied techniques such as vibration (including ultrasonic) or rotation of the cathode relativeto the solution, by pumping the electrolyte etg. catholyte through the system and over the cathode surface, by very vigorous agitation of the electrolyte by appropriately positioned propellers or other devices, etc.

In the preferred embodiment, the high relative velocity may be maintained by impinging the nickel bath against the cathode. This may be effected by impinging a stream of electrolyte uniformly against those portions of the cathode which are to be plated. In the preferred embodiment, this may be effected by directing a stream of electrolyte, as from a conduit, onto the noted portions of the cathode. If desired, a plurality of streams may be directed onto the cathode surface. Preferably in one embodiment the stream of electrolyte from the conduit may be directed against the cathode in manner to sweep the cathode surface and thereby provide fresh catholyte over the area to be plated. Preferably the impinging stream may contact the cathode at a high rate.

The nickel plate obtained by the process of this invention may be characterized by its high brightness. Typically the deposit is highly reflective over a wide current density range, and free of striations and/or hazy areas, and/or other imperfections. The luster obtained is at least comparable in every way to that obtained under normal low speed plating conditions even With the best available bright nickel additive systems.

The plate obtained by the process of this invention may be further characterized by its high leveling. Typically a one mil deposit, plated at e.g. 4060 a.s.d., will substantially obliterate scratches produced by one single pass of zero-grit emery paper when plating is eifected under high speed conditions during a period of two minutes. With the best bright nickel systems of the prior art, the best plate attainable will merely give either only partial or no obliteration of the scratch lines when the plate is deposited for the same period of time.

When phenylpropiolamide is used in combination with a secondary brightener, typically saccharin, the plate may possess an unexpectedly high ductility. This high ductility is particularly attainable when the plate is deposited from chloride-free systems. The high ductility can be produced over a reasonably wide range of concentration of phenylpropiolamide. Prior art brightener combinations permit attainment of ductile plate only under relatively narrow and difiicultly controllable concentration limits of primary brighteners.

It is a feature of this invention that the additives used may be readily determined and controlled by spectrophometric analyses in the ultraviolet region. The additives may be particularly characterized by high degree of stability under conditions of operation; any decomposition products formed do not undesirably affect the plating characteristics of the system.

Practice of this invention according to certain of its aspects may be observed from the following examples wherein all parts are expressed in grams per liter (g./l) unless otherwise indicated.

In the examples, bright high-speed nickel may be plated from a bath having the following composition:

Component Amount, g./l. Nickel sulfate 300 Nickel chloride Boric acid 45 Additive-brightener As noted infra.

Temperature 65 C.

pH As noted.

In each example, the solution was passed through a conduit obliquely ontoone end of the surface of a vertically positioned brass electrode with the section to be plated 13.5 cm. long and 1.9 cm. wide, to give an exposed cathode area of 25.7 cm. On the front of this highly polished brass cathode there was inscribed a longitudinal 1 cm. wide single pass of zero-grit emery scratches centrally positioned on the cathode surface. The back of the cathode was sealed by means of a plastic backing. The velocity of the impinging stream was about cm./ second. The angle of the downwardly flowing stream was 45 to the vertical.

The outer periphery of the cathode was bounded by plastic barriers or shields extending outwardly from the cathode thereby etfecting channelling of the electrolyte as it passed over the cathode. This entire assembly was submerged in a body of electrolyte. Cathode contact was made to that section of the strip, not to be plated, which extended out of the solution. A slab of SD nickel Was positioned parallel to the cathode at a distance of 20 cm. The times of plating used were 3 minutes (except for Example 4 where the time was 2 minutes) to give a deposit thickness of one mil. In the examples, the additive was varied.

In the following examples, the pH in Examples 1-9 It will be apparent that the novel nickel baths of this was 4 except for Example 5 where the pH was 5. The cur-' invention, which may contain as additive a composition rent density in these examples was 40 a.s.d. except for selected from the group consisting of (a) at least 0.8 Example 4where it was 60 a.s.d. g./l. of phenylpropiolamide and (b) a secondary bright- Example Amount,

Number Additive g./l. Comments 1 Phenylpropiolamide 0.6 Slight haze; highly leveled. 2 do 0. 8 Uniformly brilliant; all scratch marks virtually obliterated. 0.9 Do. 0.9 Do. (1 0.9 Do. 6 {Ph 0.3} Uniformly brilliant; all scratch Saccharin 1.6 marks virtually obliterated 0 4 good ductility. Do. 0.6 8 doi 3.2}

Pheny propio amide 0. 4 9 {Dibenzene sullonamide 3. 0} D0 1 Saturation.

In the following examples, the bath had the following ener together with 0.2-0.6 g./l. of phenylpropiolamide,

composition: permit attainment of a high speed bright nickel plate. component: Amount It will be apparent that this invention has been de- Nickfil Sulfate 375. scribed with respect to specific examples and various Boric acid 45' mcidgigftllons Will be apparent to those skilled 1n the art. As not d. Addmve e 1. The method of high speed electroplating a bright Temperature 65 C. nickel deposit Which comprises electroplating said nickel pH As noted. deposit from a nickel bath containing soluble nickel salts Current density a.s.d. and a primary brightener consisting essentially of a bright- Example I Amount, Number Additive g./l. pH Comments 10 llif iii i' ::::I:3:13:13 1: i} 4 3 3 35 highly leveled, ductile g: 4 Do. 3: 4 Do.

35 Do. g; 4.5 Do. 3 Do. g: 2 Do.

In the following examples, the bath had the following ening and leveling quantity of phenylpropiolamide as composition: the sole brightening and leveling additive present in brightening and leveling amount of at least 0.8 g./ 1., mainfi i i lfamate gg g taining the cathode current density during said plating j f IIIIIIII: at a level of at least 10 a.s.dand maintaininga high A d difive As noted. relative velocity between sald nickel bath and said cathode, thereby obtaining a highly lustrous leveled nickel Temperature C. plate over a wide cathode current density range. pH As noted. 2. The method of high-speed electroplating a bright Current density 40 a.s.d. nickel deposit as claimed in claim 1 wherein phenylpro- 352 1 1 92 Additive g lll f pH Comments 17 Phenylpropiolamide 0.9 3.5 Brilliant, highly leveled, ductile deposit. 18 targetin 91%} 3 De When examining the deposits using phenylpropiolamide piolamide is present in brightening and leveling amount as the sole additive (Examples 15) the deposits ap- 65 of 0.8 g./1.to saturation. peared to have tensile stress. Those deposits obtained 3. The method of high-speed electroplating a bright with combinations of phenylpropiolamide and a secondnickel deposit characterized by extraordinary leveling and ary brightener appeared to have lower tensile stress. Howhigh brilliance which comprises electroplating said nickel ever, in the chloride-free bath (Examples 10-18) the deposit from a nickel bath containing soluble nickel salts stress was found to be either low tensile or slightly comand a primary brightener consisting essentially of at least pressive, depending on the phenylpropiolamide concen- 0.8 g./l. of phenylpropiolamide, maintaining the cathode tration, which is highly desirable when the plated part current density at 20-60 a.s.d. during said plating, and is to be subjected to mechanical and thermal stresses maintaining a high relative velocity between said nickel during use. In the chloride-free baths of the examples, bath and said cathode.

the ductility was also markedly improved as mentioned 4. An aqueous electroyltic nickel bath for high-speed previously. electrodeposition of bright nickel plate consisting essen 9 tially of 250-500 g./l. nickel sulfate, 20-60 g./l. boric acid, and at least 0.8 g./l. of phenylpropiolamide.

References Cited UNITED STATES PATENTS 10 2,363,973 11/1944 Kennedy et a1. 204-25 2,870,709 1/1959 Boelter, Jr. 2043 OTHER REFERENCES Wesley, W. A. et al.: Electrodeposition of Nickel at 5 High Current Density, 36th Annual Proceedings of the American Electroplaters Society, pp. 79-91, 1949, TS 670 A32.

GERALD L. KAPLAN, Primary Examiner 

